Temperature shutdown

When the process stream is oil, a high bath temperature shutdown precludes the danger of coking. 

Figure 11-11 Event tree for the reactor of Figure 11-8. This includes a high-temperature shutdown system.

Instrument engineers provided a high tube-wall-temperature shutdown system to protect the heater. The initial design and prevailing practices allowed the shutdown temperature setpoint to be adjusted by the operator without any formal approval or authorization system. Perhaps the rather primitive (by todays standards) safety instrumented system had given troubles, been a nuisance, and become a victim of a one-minute modification. 

The state inside the piping room (C) was checked again and an increase in white fume was observed. Accordingly, the reactor was manually tripped at 21 20. After the trip, the reactor was cooled down by the auxiliary cooling system (ACS) and was maintained in the low-temperature shutdown state. To minimize leakage, sodium in the secondary circuit (loop C) was drained at 22 55 and drain operations were complete at 00 15, the following day. 

On Etecember 8, 1995, a leakage of sodium occurred in the piping room (C) of the Secondary Heat Transport System (SHTS) while the output of the reactor was being raised for a plant trip test at 40% output as part of a series of performance tests. The nuclear reactor was shut down manually after the accident, and sodium was drained from the SHTS in which the accident occurred and also from the Loop C of the Primary Heat Transfer System (PHTS). The plant is currently in a low-temperature shutdown state. The plant conditions of Monju at the time of the sodium leak occurrence are shown in Fig. 3.1. 

The restricting orifice and the liquid knockout pot both guard against entrainment of liquid chlorine, which might create a serious hazard in the process. The orifice, sometimes replaced by a flow control valve, limits the flow to no more than the vaporizing capacity and so helps to avoid entrainment. Other possible measures include a high-level shutdown on the vaporizer and gas temperature control or low-temperature shutdown. The knockout pot is the second line of defense. 

In waste handling facilities, activated carbon adsorption units can be overheated to ignition temperatures. These systems should be protected by detonation arresters and high bed temperature shutdowns. 

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